Ionizers are already known that alternately apply a positive and negative high voltage to a discharge electrode such as a discharge needle so as to generate ions of positive and negative polarities, thereby electrically neutralizing a charged work. The ionizer of this type generally includes, as disclosed in Patent Literature (PTL) 1, the discharge electrode and a power supply controller including a high voltage generation circuit that outputs the positive and negative high voltage to the discharge electrode, the discharge electrode and the power supply controller being integrally incorporated in a housing. Such a configuration inevitably leads to an increase in outer dimensions of the housing, and may thereby disable the ionizer from being installed at a desired location when the space availability of the intended location is limited.
To cope with such a drawback, for example PTL 2 discloses an ionizer in which an electrode unit is formed by locating the discharge electrode a different housing from the power supply controller, and the housing of the discharge electrode is formed in a smaller size, so that the discharge electrode can be installed separately from the power supply controller. In this case, a shielded cable may be employed for the electrical connection between the power supply controller and the electrode unit, and the cable generally includes an insulating layer interposed between the conductor and the shield layer.
Here, the amount of ion generated from the discharge electrode in the ionizer is proportional to an integral value of the voltage waveform actually applied to the electrode, and therefore, for example when the power supply controller outputs a pulsating voltage, it is preferable that the voltage is applied to the discharge electrode with the pulse waveform maintained to a maximum possible extent.
However, in the mentioned shielded cable a kind of capacitor (so called virtual capacitor) is formed between the conductor and the shield layer, and hence an electrostatic capacitance, acting as a floating capacitance (parasitic capacitance), is generated in the shielded cable itself. Accordingly, even though a voltage of such a pulse waveform as represented by solid lines in FIG. 7 is outputted from the power supply controller, the voltage waveform actually inputted in the electrode unit (i.e., applied to the discharge electrode) is deformed as shown in FIG. 8 owing to a response delay originating from the electrostatic capacitance, and consequently the ion generation efficiency is degraded. Such an impact of the floating electrostatic capacitance in the cable on the ion generation efficiency is pointed out also in PTL 3 and PTL 4.    [PTL 1] Japanese Unexamined Patent Application Publication No. 2011-014319    [PTL 2] Japanese Unexamined Patent Application Publication No. 2012-252800    [PTL 3] Japanese Unexamined Patent Application Publication No. 2011-009167    [PTL 4] Japanese Unexamined Patent Application Publication No. 2011-009168